265 



fissures.* is a question on which 1 cannot hnxard an opinion, 

 owing to my own want of personal knowledge of the subject. 



According to the admirable observations of Leopold von 

 Buch, the masses of dolomite found in Southern Tyrol, and on 

 the Italian side of the Alps, present the most remarkable 

 instance of metamorphism produced by massive eruptive rocks 

 on compact calcareous beds. This transformation of the lime- 

 stone seems to have proceeded from the fissures which traverse 

 it in all directions. The cavities are everywhere covered with 

 rhomboidal crystals of magnesian bitter-spar, and the whole 

 formation, without any trace of stratification or of the fossil 

 remains which it once contained, consists only of a granular 

 aggregation of crystals of dolomite. Talc laminae lie scattered 

 here and there in the newly formed rock, traversed by masses 

 of serpentine. In the valley of the Fassa, dolomite rises per- 

 pendicularly in smooth walls of da/xling whiteness to a height 

 of many thousand feet. It forms sharply-pointed conical 

 mountains, clustered together in large numbers, but yet not in 

 contact with each other. The contour of their forms recall to 

 mind the beautiful landscape, with which the rich imagination 

 of Leonard! da Vinci has embellished the background of the 

 portrait of Mona Lisa. 



The geognostic phenomena which we are now describing, 

 and which excite the imagination, as well as the powers ot 

 the intellect, are the result of the action of augitic porphyry 

 manifested in its elevating, destroying, and transforming 

 force, f The process, by which limestone is converted into 

 dolomite, is not regarded by the illustrious investigator, who 

 first drew attention to the phenomenon, as the consequence of 

 the talc being derived from the black porphyry, but rather as 

 a transformation, simultaneous with the appearance of this 

 erupted stone through wide fissures filled with vapours. It 

 remains for future enquirers to determine how transformation 

 jan have been effected without contact with the endogenous 



* According to the assumption of an excellent ana very experienced 

 observer, Karl von Leonhard; see his Jahrbuch fur Mineralogie, 1834, 

 B. 329, and Bernhard Cotta, Q-eognosie, s J10. 



t Leop. von Buch, Geognostiscke Bi lej'e an A lex. von Humboldt, 

 182*, s. 36 and 82 ; also in the Annaler, de Chemie, t. xxiii. p. 276, arid 

 iu the Abhandl der Berliner Akad. a,^ der J. 1822 und 1S23, s. 8* 

 136; von Dechen, Geognosie, s. 574-570. 



